1. Field of the Invention
The present invention relates to a flexible, non-metallic conveyor belt structure for a conveyor belt that carries materials or items between adjacent stations in a sequentially-based processing system. More particularly, the present invention relates to a flexible, non-metallic conveyor belt structure for conveying hot, tacky materials and that provides greater resistance to longitudinal stretching of the belt structure when subjected to heat that is transferred to the belt from the heated material being conveyed.
2. Description of the Related Art
Flexible conveyor belts formed from several layers of woven fabrics that are embedded in a rubber matrix are well known. Typical fabric materials include cotton, cotton/polyester, and other polymer-based yarns that are woven to define generally rectangular layers or plies of the belt. Rubber skim is provided between the fabric layers and also on the upper and lower surfaces of the belt material to cover and enclose the inner layers of fabric. The rubber is subjected to a vulcanization process, and the longitudinal ends of the belt material are spliced together to form an endless loop that is adapted to pass around a pair of spaced, parallel drums or rollers, at least one of which is a driven drum or roller, to define a conveying path for the materials or articles that are to be conveyed.
Many of the known belt structures are intended to convey materials or articles that are not heated to a significant degree. However, when hot materials are conveyed, the tensile loads applied by the belt drive mechanism to common, commercially available conveyor belt structures are such that the belts tend to stretch longitudinally. Longitudinal stretching results in loosening of the belt relative to the drums or rollers around which or over which the belt passes.
When a conveyor belt becomes loose as a result of longitudinal stretching of the belt, an adjustment must be made to the belt in order for the belt to continue to be under tension, so it can be driven by the belt drive mechanism. One possible type of adjustment involves increasing the relative spacing of the belt drive drums or rollers to accommodate the longer belt loop length. Another possible type of adjustment involves shortening of the belt length in order to maintain the belt tension that is needed to provide the required degree of surface-to-surface contact force between the belt and the belt drive system for continued belt movement in the desired direction.
Drum or roller spacing adjustment requires displacing the parallel axes of the drums or rollers away from each other. The displacement is needed in order to maintain firm surface contact of the belt on the drums or rollers, and thereby maintain sufficient belt tension so that the belt continues to be driven and to move in the desired direction to convey the materials or articles of interest. However, drum or roller axis displacement is not practical in many cases because the belt drive system is generally fixed in relation to the floor, or is fixed relative to other structural elements of the conveyor system.
The other way to overcome the effects of belt stretching when conveyor belts are subjected to high temperatures by virtue of carrying hot materials is to reduce the longitudinal length of the stretched belt to substantially its original length. The intent is to eliminate the additional belt length that is caused by the stretching of the belt material. The belt length is reduced by cutting a portion of the belt material so that the belt is again substantially at its initial longitudinal length, and then resplicing the belt by connecting together by known methods the belt ends that result from the belt cutting operation. However, resplicing of a stretched belt requires that the production line in which the conveyor belt is located be stopped, that the belt be removed from the conveyor system, that a section be cut from the belt, that the belt ends at the cuts be respliced, and that the belt then be reinstalled on the conveyor drive system drums or rollers. The resplicing operation results in undesired down time for the production line involved, reducing the output of the line, and thereby increasing the costs of the production operation.
In the production of rubber products, such as automobile tires and other molded rubber items, hot, tacky rubber is required to be transported between production stations on a continuous, around-the-clock basis. The temperature of the rubber material being conveyed can typically range from about 300° F. to about 330° F. Conventional cotton/polyester fabric-based conveyor belts that have been utilized in such high temperature rubber processing operations have been found to have a limited effective operating life, of the order of only about 12 weeks or so. Moreover, and significantly, such conventional belts stretch during use under those high temperature processing conditions. Typically, at least one and sometimes two belt splicings are required during that 12 week time span in order to shorten the belts by reducing their longitudinal length so that they can continue to be used. But each of the splicing operations require an undesirable production line shutdown, which causes expensive production line downtime affecting the entire production operation for the tires or other rubber products that are being produced.
There is therefore a need for an improved conveyor belt structure that exhibits greater resistance to longitudinal stretching when carrying hot, tacky materials, and that provides a longer effective belt operating lifetime with fewer production line shutdowns.